Simmer mustard greens in salted water until tender, 5 minutes. Drain and chop coarsely. In a large skillet, fry bacon until the ends are crisp. Add onion and garlic to the pan; cook until onions are translucent, about 3 minutes. Add a pinch of red pepper flakes and the marjoram. Deglaze with beer. Reduce sauce until it reaches the consistency of a light syrup, about 3-4 minutes. Add the beans and mustard greens; turn heat down to medium-low and cover. Cook for an additional 5 minutes or until greens are cooked through. Check seasoning. Serve immediately, passing grated cheese at the table.